U.S. Pat. No. 8,179,816 discloses an indoor positioning system using a narrowband radio frequency transceiver and discussed a number of other indoor positioning systems. For example, some systems use power-of-arrival (PoA) from a set access points in accordance with IEEE 802.11 for wireless local area networks to determine the location of a mobile device. For example, some systems use Time-of-flight (ToF) of signals from or to satellites or base-stations to convert the arrival time to distances in view of the propagation speed of signals.
U. S. Pat. App. Pub. No. 2012/0226467 discloses an inertial navigation unit that utilizes multiple accelerometers to gather specific force data for improvement of the initialization, navigation, assistance, or corrective processes.
U.S. Pat. App. Pub. No. 2002/0198656 discloses an Inertial GPS navigation system that has a GPS sub-system and an inertial sub-system. If the receiver loses GPS satellite signals, the receiver utilizes the inertial position, velocity and covariance information to speed up GPS satellite signal re-acquisition and associated ambiguity resolution operations.
U.S. Pat. App. Pub. No. 2012/0173139 discloses the use of magnetic fingerprint of locations to estimate the position of a navigation device.
The disclosures of the above discussed patent documents are hereby incorporated herein by reference.